<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>菜鸟教程(runoob.com)</title>
</head>
<body>

<p>点击按钮，在等待 3 秒后弹出 "Hello"。</p>
<button onclick="myFunction()">点我</button>

<script>
    function myFunction()
    {
        setTimeout(
            function(){alert("Hello")},

            3000);
    }



    //定时任务
    window.setInterval(showalert, 2000);

    var num=1;
    function showalert() {
        console.log(num);
        num++;
    }
</script>

</body>
</html>